src/shared/pager.c

   1 /*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
   2
   3 /***
   4   This file is part of systemd.
   5
   6   Copyright 2010 Lennart Poettering
   7
   8   systemd is free software; you can redistribute it and/or modify it
   9   under the terms of the GNU Lesser General Public License as published by
  10   the Free Software Foundation; either version 2.1 of the License, or
  11   (at your option) any later version.
  12
  13   systemd is distributed in the hope that it will be useful, but
  14   WITHOUT ANY WARRANTY; without even the implied warranty of
  15   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  16   Lesser General Public License for more details.
  17
  18   You should have received a copy of the GNU Lesser General Public License
  19   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  20 ***/
  21
  22 #include <fcntl.h>
  23 #include <stdlib.h>
  24 #include <unistd.h>
  25 #include <string.h>
  26 #include <sys/prctl.h>
  27
  28 #include "pager.h"
  29 #include "util.h"
  30 #include "process-util.h"
  31 #include "macro.h"
  32 #include "terminal-util.h"
  33 #include "signal-util.h"
  34 #include "copy.h"
  35
  36 static pid_t pager_pid = 0;
  37
  38 noreturn static void pager_fallback(void) {
  39         int r;
  40
  41         r = copy_bytes(STDIN_FILENO, STDOUT_FILENO, (uint64_t) -1, false);
  42         if (r < 0) {
  43                 log_error_errno(r, "Internal pager failed: %m");
  44                 _exit(EXIT_FAILURE);
  45         }
  46
  47         _exit(EXIT_SUCCESS);
  48 }
  49
  50 int pager_open(bool jump_to_end) {
  51         _cleanup_close_pair_ int fd[2] = { -1, -1 };
  52         const char *pager;
  53         pid_t parent_pid;
  54
  55         if (pager_pid > 0)
  56                 return 1;
  57
  58         if (!on_tty())
  59                 return 0;
  60
  61         pager = getenv("SYSTEMD_PAGER");
  62         if (!pager)
  63                 pager = getenv("PAGER");
  64
  65         /* If the pager is explicitly turned off, honour it */
  66         if (pager && (pager[0] == 0 || streq(pager, "cat")))
  67                 return 0;
  68
  69         /* Determine and cache number of columns before we spawn the
  70          * pager so that we get the value from the actual tty */
  71         (void) columns();
  72
  73         if (pipe(fd) < 0)
  74                 return log_error_errno(errno, "Failed to create pager pipe: %m");
  75
  76         parent_pid = getpid();
  77
  78         pager_pid = fork();
  79         if (pager_pid < 0)
  80                 return log_error_errno(errno, "Failed to fork pager: %m");
  81
  82         /* In the child start the pager */
  83         if (pager_pid == 0) {
  84                 const char* less_opts, *less_charset;
  85
  86                 (void) reset_all_signal_handlers();
  87                 (void) reset_signal_mask();
  88
  89                 (void) dup2(fd[0], STDIN_FILENO);
  90                 safe_close_pair(fd);
  91
  92                 /* Initialize a good set of less options */
  93                 less_opts = getenv("SYSTEMD_LESS");
  94                 if (!less_opts)
  95                         less_opts = "FRSXMK";
  96                 if (jump_to_end)
  97                         less_opts = strjoina(less_opts, " +G");
  98                 setenv("LESS", less_opts, 1);
  99
 100                 /* Initialize a good charset for less. This is
 101                  * particularly important if we output UTF-8
 102                  * characters. */
 103                 less_charset = getenv("SYSTEMD_LESSCHARSET");
 104                 if (!less_charset && is_locale_utf8())
 105                         less_charset = "utf-8";
 106                 if (less_charset)
 107                         setenv("LESSCHARSET", less_charset, 1);
 108
 109                 /* Make sure the pager goes away when the parent dies */
 110                 if (prctl(PR_SET_PDEATHSIG, SIGTERM) < 0)
 111                         _exit(EXIT_FAILURE);
 112
 113                 /* Check whether our parent died before we were able
 114                  * to set the death signal */
 115                 if (getppid() != parent_pid)
 116                         _exit(EXIT_SUCCESS);
 117
 118                 if (pager) {
 119                         execlp(pager, pager, NULL);
 120                         execl("/bin/sh", "sh", "-c", pager, NULL);
 121                 }
 122
 123                 /* Debian's alternatives command for pagers is
 124                  * called 'pager'. Note that we do not call
 125                  * sensible-pagers here, since that is just a
 126                  * shell script that implements a logic that
 127                  * is similar to this one anyway, but is
 128                  * Debian-specific. */
 129                 execlp("pager", "pager", NULL);
 130
 131                 execlp("less", "less", NULL);
 132                 execlp("more", "more", NULL);
 133
 134                 pager_fallback();
 135                 /* not reached */
 136         }
 137
 138         /* Return in the parent */
 139         if (dup2(fd[1], STDOUT_FILENO) < 0)
 140                 return log_error_errno(errno, "Failed to duplicate pager pipe: %m");
 141         if (dup2(fd[1], STDERR_FILENO) < 0)
 142                 return log_error_errno(errno, "Failed to duplicate pager pipe: %m");
 143
 144         return 1;
 145 }
 146
 147 void pager_close(void) {
 148
 149         if (pager_pid <= 0)
 150                 return;
 151
 152         /* Inform pager that we are done */
 153         stdout = safe_fclose(stdout);
 154         stderr = safe_fclose(stderr);
 155
 156         (void) kill(pager_pid, SIGCONT);
 157         (void) wait_for_terminate(pager_pid, NULL);
 158         pager_pid = 0;
 159 }
 160
 161 bool pager_have(void) {
 162         return pager_pid > 0;
 163 }
 164
 165 int show_man_page(const char *desc, bool null_stdio) {
 166         const char *args[4] = { "man", NULL, NULL, NULL };
 167         char *e = NULL;
 168         pid_t pid;
 169         size_t k;
 170         int r;
 171         siginfo_t status;
 172
 173         k = strlen(desc);
 174
 175         if (desc[k-1] == ')')
 176                 e = strrchr(desc, '(');
 177
 178         if (e) {
 179                 char *page = NULL, *section = NULL;
 180
 181                 page = strndupa(desc, e - desc);
 182                 section = strndupa(e + 1, desc + k - e - 2);
 183
 184                 args[1] = section;
 185                 args[2] = page;
 186         } else
 187                 args[1] = desc;
 188
 189         pid = fork();
 190         if (pid < 0)
 191                 return log_error_errno(errno, "Failed to fork: %m");
 192
 193         if (pid == 0) {
 194                 /* Child */
 195
 196                 (void) reset_all_signal_handlers();
 197                 (void) reset_signal_mask();
 198
 199                 if (null_stdio) {
 200                         r = make_null_stdio();
 201                         if (r < 0) {
 202                                 log_error_errno(r, "Failed to kill stdio: %m");
 203                                 _exit(EXIT_FAILURE);
 204                         }
 205                 }
 206
 207                 execvp(args[0], (char**) args);
 208                 log_error_errno(errno, "Failed to execute man: %m");
 209                 _exit(EXIT_FAILURE);
 210         }
 211
 212         r = wait_for_terminate(pid, &status);
 213         if (r < 0)
 214                 return r;
 215
 216         log_debug("Exit code %i status %i", status.si_code, status.si_status);
 217         return status.si_status;
 218 }